1. Field of the Invention
The present invention relates to a nuclear magnetic resonance imaging apparatus for obtaining an image of a section of an inspected portion of a subject by means of the principle of nuclear magnetic resonance and, more particularly, to an automatic aligning mechanism used to automatically align the inspected portion of the subject at an inspecting position of the imaging apparatus.
2. Description of the Related Art
As shown in FIG. 1, a conventional nuclear magnetic resonance imaging apparatus has a gantry 16 which supports a hollow-shaped main coil 12, a hollow-shaped gradient coil 14 coaxially disposed in the hollow region of the hollow-shaped main coil 12, and a transmitting/receiving coil 15. The main coil 12 is used for applying a static magnetic field to a subject 10, such as a patient, located in its hollow region 1, the gradient coil 14 is used for generating a gradient magnetic field to obtain position information of a portion, at which a nuclear magnetic resonance signal is induced, in the patient 10 located in the static magnetic field 1, and the transmitting/receiving coil 15 is used for transmitting/receiving the nuclear magnetic resonance signal from the inspected portion of the patient 10. The gantry 16 is mounted, for example, on a floor of a hospital.
The gantry 16 has an opening 18 corresponding to the hollow region of the main coil 12 and the gradient coil 14, and the subject 10 is inserted into the opening 18 of the gantry 16 so that the subject 10 is located in the hollow region of the main coil 12 and the gradient coil 14.
The nuclear magnetic resonance imaging apparatus has a bed 20 for inserting the subject 10 into the opening 18 of the gantry 16.
The bed 20 is disposed in the vicinity of the opening 18 on the extension line of the opening 18 of the gantry 16 on the floor, and has a table top 22 being movable along the extension line. The bed 20 can move the table top 22 in upward and downward directions so that the patient 10 can easily ride on or get down from the table top 22.
A light projector 24 extending above the extension line is mounted on the gantry 16 at the side of the bed 20.
In order to obtain an image of a section of an inspected portion 10a of the patient 10 by means of the principle of a nuclear magnetic resonance in the abovementioned conventional apparatus, the patient 10 is first laid at a predetermined position on the upper surface of the table top 22 in a state that the patient 10 is directed upward, and the table top 22 is set at the same vertical level as the center line of the opening 18 of the gantry 16.
Then, the table top 22 is moved toward the opening 18 of the gantry 16 until a light beam 26 projected downward from the light projector 24 projects onto the inspected portion 10a of the patient 10 laid on the upper surface of the table top 22. When the inspected portion 10a of the patient 10 is completely aligned to the light beam 26 from the light projector 24, the movement of the table top 22 in a direction along the extension line is stopped temporarily.
A center line 30 in the longitudinal direction of the main coil 12 is an inspecting position in the abovementioned apparatus. After the alignment of the inspected portion 10a of the patient 10 with respect to the light beam 26 from the light projector 24 is finished, the movement of the table top 22 is restarted. The table top 22 is moved along the extension line into the opening 18 for a predetermined distance in a direction along the extension line between the inspecting position 30 and the light projector 24, and automatically stopped. By the restarting and the stop, following the restarting, of the movement of the table top 22, the inspected portion 10a of the patient 10 laid on the upper surface of the table top 22 is brought into coincidence with the inspecting position 30 in the above-described apparatus as shown in FIG. 2.
Thereafter, when the above-mentioned apparatus performs a predetermined operation necessary to obtain a nuclear magnetic resonance image, a section of the inspected portion 10a of the patient 10 is imaged in the above-described apparatus by means of the principle of nuclear magnetic resonance, the image is displayed on a display (not shown) of the above-mentioned apparatus, and recorded in a recorder (not shown) of the apparatus as required.
When a desired image of the section of the inspected portion 10a is obtained, the table top 22 is returned to its initial position located outside the opening 18 of the gantry 16 without being stopped, and the patient 10 on the table top 22 may get down from the upper surface of the table top 22 at the initial position.
In the conventional nuclear magnetic resonance imaging apparatus constructed and operated as described above, the table top 22 must be temporarily stopped so that the inspected portion 10a of the patient 10 is brought into coincidence with the light beam 26 from the light projector 24. The table top 22 is moved from the initial position of the table top 22, located outside the opening 18 of the gantry 16 and at which the patient 10 is laid at a predetermined portion on the upper surface of the table top 22, into the opening 18 of the gantry 16, and is stopped at a position in which the inspected portion 10a of the patient 10 on the upper surface of the table top 22 is brought into coincidence with the inspecting position 30 in the above-described apparatus. Further, in order to accurately bring the inspected portion 10a into coincidence with the light beam 26 from the light projector 24, the moving speed of the table top 22 must be decelerated as the inspected portion 10a approaches the light beam 26.
Therefore, in the above-mentioned conventional nuclear magnetic resonance imaging apparatus, the abovedescribed temporary stop of the table top 22 and the deceleration of the moving speed of the table top 22 in the vicinity of the temporary stop are both necessary while the table top 22 is moved from the initial position to the inspecting position. However they disturb the shortening of a time required to complete the procedures during which the patient 10 is laid at a predetermined position on the upper surface of the table top 22 at the initial position, the inspected portion 10a of the patient 10 is brought into coincidence with the inspecting position 30 in the abovedescribed apparatus, the section of the inspected portion 10a is imaged, and the table top 22 is returned to the initial position.
The aligning work of the inspected portion 10a with respect to the light beam 26 is troublesome in that it generates a spiritual stress of operator of the abovedescribed apparatus.
In the operation of the expensive nuclear magnetic resonance imaging apparatus, the more the number of patients which are inspected per unit of time, the better. The above-described circumstances in the conventional nuclear magnetic resonance imaging apparatus disturbs the intention to improve the number of the patients to be inspected per unit of time.